That is incorrect. It has nothing to do with Apple, and if that is what they are saying that is purely to give you the runaround.
It is an issue with how CEC functions on their TV. Each manufacturer has their own implementation. CEC exists not only to pair with remote controls but also to communicate between devices (i.e. switch on Apple TV, also power on TV and switch inputs).
CEC is merely a protocol that Apple TV accesses, the same could occur no matter what device you had connected to your TV.
Roku is simply the smart TV platform running on the TV. Whether a TV is smart or not has no bearing on how Apple TV functions.
The iPhone app works over Wifi.